1. Field of the Invention
This invention relates ammunition and more particularly to a low toxicity composite bullet and a composite low toxicity material useful in manufacture of bullets and other high dentistry applications where toxicity of lead is a concern. Another aspect of this invention relates to a material which has an elastic matrix and a relatively plastic metal filler characterized by a relatively high density.
2. Related Art
The use of lead bullets is known. These can be of several currently available types. One is a copper jacketed lead bullet which is basically identical to service ammunition. Another is a solid lead bullet and still another is a frangible composite lead gallery bullet.
Also known are composite bullets of materials other than lead such the copper frangible gallery bullet of U.S. Pat. No. 5,237,930 issued Aug. 24, 1993 to Belanger et al. Such composite bullets are characterized by the use of powders of various metals other than lead consolidated into a bullet having sufficient strength for use and intended to be disrupted into small fragments on impact with a gallery target.
The costs associated with the training of users of ammunition can be extremely high.
Airborne lead contamination is associated with the use of conventional ammunition. During a shooting session, there is an emission of lead dust into the atmosphere. Measurements of airborne lead, taken at various periods of time in different target ranges have definitely established that high lead concentrations exist. It has also been determined that these concentrations, in many cases, are well above the minimum safe level for human consumption. The concentration of airborne lead is dependent upon several variables such as; the volume of air removed from the range on a continuous basis, amount of cartridges fired per hour, size of the facility, and cartridge type. As may be appreciated, changing some of these variables would involve large capital expenditures, the money for which is simply not available for the purpose of reducing airborne lead, especially considering that many of the ranges are financed by private range owners who are limited in what they can charge their customers. The simple political solution for private ranges is to close them down by edict. This deprives the ordinary citizen of his or her right to keep and bear arms because if he or she cannot practice, he or she becomes ineffective and therefore unsafe and dangerous to others. The solution for police and military is not nearly as simple. They must be able to practice in order to be proficient and safe to the populace. Because of geography, or capital expense, they are forced to practice in unsafe conditions.
Airborne lead comes from the following sources: (1) lead from the lead styphnate in primer mixes, (2) lead from the base of the bullet exposed briefly to high propellant combustion temperatures, (3) lead removed by the lands and grooves of the barrel as the bullet moves, and (4) lead from the impact zone behind the targets.
In large caliber bullets most of the airborne lead in the target range can be prevented by using a copper jacket at the base (rear end) and bourrelet of the bullet and using a lead free primer, airborne lead still occurs, however, at the target. Copper jackets are not suitable for small caliber ammunition such as 0.22 rimfire because the jacket makes it difficult to crimp and takes up volume thus reducing projectile density.
The use of other materials has been examined an depth. The principle problems with other materials are density, strength and cost. Few materials equal or exceed lead in density and those that do are, comparatively, quite expensive or have too little or too much strength. Copper is the closest of the materials available at moderate cost increase, but is simply too low an density. U.S. Pat. No. 5,127,322 issued Aug. 24, 1993 to Belanger et al. discloses a copper and nylon composite frangible bullet with a density of slightly over 50% of the density of lead in the bullets sought to be duplicated. As a result, Belanger et al had to redesign both the bullet and cartridge case of the ammunition in which it was used in order to achieve operability of some of the weapons with which the projectile might be used.
In order for a round to cycle an autoloader, a minimum amount of energy must be delivered to the cycling mechanism. For some types of weapons, this energy as delivered by the expanding gases pushing back the receiver as in the Colt 0.45 ACP pistol for example. For others, high pressure gas behind the bullet passes through a port inside the barrel to the cycling mechanism as in the Colt M16 rifle.
Propellant powders are designed to work with a projectile of a certain mass that provides a typical pressure-vs-time curve. Using a lighter projectile will also cause problems, the main one being too low an energy transfer to give the feeding mechanism the needed momentum to cycle in certain types of weapons at standard velocity regimes. Thus, with lighter projectiles, to make recoil mechanisms of many currently used guns function, the projectiles have to be made to go much faster to provide sufficient energy transfer. This requires powders that burn faster. The combination of fast powders and lightweight projectiles can dangerously exceed recognized chamber pressure standards. The higher than design linear velocities of the bullets are inherently coupled with higher than design spin velocities thus resulting in poorer accuracy and increased centrifugal forces. With these less dense materials, the bullet cannot be brought up to its former weight by increasing its length forward of the cartridge case due to the dimensional limitations imposed by the standard gun chambers into which the bullet must fit. A bullet that would require rechambering the gun would not be acceptable to many gun owners because the weapon would no longer be optimal for standard ammunition. Increasing bullet volume by extending the bullet length further into the cartridge case is not acceptable because most modern cartridges are fully loaded with powder and this would require either substantially altering the powder speed (changing powder type) or decreasing velocity and thus either exceeding chamber pressure standards and chancing blowing up the gun or having it fail to function. Neither of these choices are commercially viable.
For bullets, lower density almost invariably translates into poorer performance in terms of accuracy. Needless to say, an inaccurate bullet is not a marketable item.
Ideally, a material is sought which has the same or very close to the same density as lead, yet which does not allow significant airborne lead to occur in the target range. The present invention provides that material.